This application claims the priority of Application No. 101 49 121.2-12, filed Oct. 5, 2001, in Germany, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an energy-absorbing bumper with a structural part, which is arranged underneath an outer skin or shell with soft impact characteristics, supports the outer skin in a flexible manner and has a cross section that differs from the cross section of the outer skin or shell.
A bumper of this kind known from German Patent Document DE 25 05 169 A1 has a structural part made from elastic waste product components, which are embedded in a binder, in particular a reaction resin.
In the case of a bumper illustrated by way of example in DE 25 05 169 A1, the outer casing or shell comprises two separate shell components, which are very largely symmetrical with respect to a horizontal plane and are arranged as cantilevers in the region of a contact zone, which is the first to be subjected to loading when the vehicle collides with a pedestrian.
In German Patent Document DE 17 55 512 A and corresponding U.S. Pat. No. 3,836,192 covering parts of the outer surface of the outer skin of the vehicle are disclosed, in particular a passenger vehicle, that are at risk of impact with an elastically and/or plastically flexible plastic, in particular a foam. The hardness of the plastic layer may possibly decrease from the outside inwards. Hollow chambers, which are filled with a fluid that can yield when subjected to impact, are furthermore formed at particularly exposed locations, e.g. bumpers or front or rear flaps.
In European Patent Document EP 1 046 546 A1 a bumper designed essentially as a foam component is described. This bumper can have a central and an upper region that are set back relative to a lower edge region. Provision is furthermore made to design the lower region with increased stiffness. This is intended to ensure that collision forces take effect preferentially at a low level above the roadway in the event of accidents involving pedestrians.
According to German Patent Document DE 30 09 571 A1, the frontal area of a road vehicle, in particular a tram, is designed in such a way that, in the event of a collision with the vehicle, there is no possibility or a significantly reduced likelihood of a pedestrian being thrown to the side.
Finally, European Patent Document EP 0 734 908 A2 and corresponding U.S. Pat. No. 5,785,367 discloses a bumper that is designed as a beam and is supported on the longitudinal members of the body of a vehicle via deformation members of the impact-absorber type.
An aspect of the invention is to provide a bumper that is optimized with respect to the protection of pedestrians in collisions with the vehicle.
According to certain preferred embodiments of the invention, this aspect is achieved with a bumper of the type stated at the outset by virtue of the fact that the structural part is composed of foam capable of deformation and energy-absorbing compression or of a material having similar properties and a space-lattice structure that can be crushed in a manner that involves energy absorption, and is arranged between an impact or contact zone of the outer skin or shell and a rear side of the bumper facing away from the latter and having a cross section that differs from the outer skin or shell of the bumper.
The general idea of providing a very wide degree of freedom in the design of the shape of the outer skin or shell of the bumper and especially of designing the structural part with a resistance characteristic that is the optimum in collisions with pedestrians is provided. Since cross-sectional areas are left free by the structural part within the cross section of the outer skin or shell of the bumper, the material of the structural part can also be displaced quasi-hydraulically in a collision before the cross section of the generally relatively inelastic outer skin or shell, which is reduced by the respective collision, is completely filled by the material of the structural part. After the filling, absorption of the collision energy can take place basically only through the compressibility of the material of the structural part. In general, the quasi-hydraulic displacement of material and compression or crushing of the material of the structural part will take place simultaneously.
Owing to the difference in the cross sections of the outer skin or shell in the case of a flexible structural part, there is furthermore the advantage that the outer skin or shell will be displaced comparatively slightly in a tangential direction relative to the outer plane in the collision, thus enabling the consequences of a collision for a pedestrian to be significantly reduced even when the direction of the collision has a pronounced tangential component relative to the outer surface.
According to a particularly preferred embodiment of the invention, a reinforcing inner part, which can expediently be in the form of a flat strip, is arranged on the rear side of the bumper. As a result, collision forces which may be affecting a small area on the outside of the bumper are dissipated to vehicle components arranged behind the bumper over a comparatively large area.
The arrangement of the reinforcing inner part is particularly expedient if the bumper rests by way of this inner part on a beam capable of deformation in an energy-absorbing manner, which is intended generally not to be deformed when the vehicle collides with a pedestrian but to yield only in the case of higher forces.
This is because, especially in combination with the reinforcing inner part, it is possible to ensure that the beam yields inelastically only at a collision or impact energy exceeding a higher threshold and that the maximum degree of deformation of the structural part upon loading of a predetermined collision or contact area is used up only in the case of impact energy exceeding this threshold. Ultimately, this is equivalent to saying that, although collision forces acting on small areas of the outside can deform the bumper into the vicinity of its rear side, they cannot readily deform the beam as well.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompany drawings.